Hyponatremia

Hyponatremia Symptoms

Patients with low-level, chronic water intoxication are often asymptomatic, but may have symptoms related to the underlying cause.

Severe hyponatremia in acute or chronic form may cause osmotic shift of water from the plasma into the brain cells. Typical symptoms include nausea, vomiting, headache and malaise. As the hyponatremia worsens, confusion, diminished reflexes, convulsions, stupor or coma may occur. Since nausea is, itself, a stimulus for the release of ADH, which promotes the retention of water, a positive feedback loop may be created and the potential for a vicious cycle of hyponatremia and its symptoms exists.

A feedback loop can also be created by severe thirst, which is a symptom of some hyponatremic individuals. When these people consume large quantities of water without an adequate increase in sodium, the hyponatremic condition worsens.

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Hyponatremia Causes

An abnormally low plasma sodium level is best considered in conjunction with the person's plasma osmolality and extracellular fluid volume status. Indeed, correct ascertainment of volume status, as well as determination of the presence or absence of edema, are both critical in establishing the cause of hyponatremia. As described above, a state of volume depletion leads to increased blood levels of ADH and thus water retention.

The greater the amount of water that is retained, the more the blood sodium will become diluted to cause worsening degrees of hyponatremia. The presence of edema indicates that blood volume has been lost insofar as fluid from the blood has shifted out into the peripheral tissues to cause the edema. In other words, edema is usually reflecting a state of blood volume depletion. As a result, edematous states are also associated with increased blood levels of ADH, water retention, and hyponatremia. In all cases of volume depletion-associated hyponatremia, it is important to note that retention of water ''per se'', such as that promoted by ADH, does not correct the volume depleted state.

In addition to volume depletion, there are other causes of increased ADH levels (and ultimately, therefore, of hyponatremia). These include nausea, pain, and opiate drugs such as codeine and morphine. Such factors often play a role in the hyponatremia that is frequently seen in hospitalized patients.

TypeSerum osmolality (mOsm/kg)Description
Hypotonic hyponatremia< 280When the plasma osmolality is low, the extracellular fluid volume status may be in one of three states: low volume, normal volume, or high volume.
Isotonic hyponatremiabetween 280 and 295Certain conditions that interfere with laboratory tests of serum sodium concentration (such as extraordinarily high blood levels of lipid or protein) may lead to an erroneously low ''measurement'' of sodium. This is called pseudohyponatremia.
Hypertonic hyponatremia> 295Hypertonic hyponatremia can be associated with shifts of fluid due to osmotic pressure.

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Hyponatremia - What is Hyponatremia?

Hyponatremia (British: ''hyponatraemia'') is an electrolyte disturbance (a disturbance of the salts in the blood) in which the sodium (''Natrium'' in Latin) concentration in the plasma is lower than normal (''hypo'' in Greek), specifically below 135 mEq/L. The large majority of cases of hyponatremia occurring in adults result from an excess amount or effect of the water retaining hormone known as Antidiuretic Hormone commonly abbreviated as ADH.

Hyponatremia is most often a complication of other medical illnesses in which either fluids rich in sodium are lost (for example because of diarrhea or vomiting), or excess water accumulates in the body at a higher rate than it can be excreted (for example in polydipsia (rarely) or syndrome of inappropriate antidiuretic hormone, SIADH). Regarding sodium loss as a cause of hyponatremia, it is important to note that such losses promote hyponatremia only in an indirect manner. In particular, hyponatremia occurring in association with sodium loss does not reflect inadequate sodium availability as a result of the losses. Rather, the sodium loss leads to a state of volume depletion, with volume depletion serving as a signal for the release of ADH. As a result of ADH-stimulated water retention, blood sodium becomes diluted and hyponatremia results.

There may also be spurious hyponatremia (pseudohyponatremia or factitious hyponatremia) if other substances expand the serum and dilute the sodium (for example, high blood sugar (hyperglycemia) or if a blood constituent leads to the creation of a sodium-free phase in the blood thereby causing the blood plasma volume to be overestimated (e.g. extreme hypertriglyceridemia).

Hyponatremia can also affect athletes who consume too much fluid during endurance events, people who fast on juice or water for extended periods and people whose dietary sodium intake is chronically insufficient.

The diagnosis of hyponatremia relies mainly on the medical history, clinical examination and blood and urine tests. Treatment can be directed at the cause (for example, corticosteroids in Addison's disease) or involve restriction of water intake, intravenous saline or drugs like diuretics, demeclocycline, urea or vaptans (antidiuretic hormone receptor antagonists). Correcting the salt and fluid balance needs to occur in a controlled fashion, as too rapid correction can lead to severe complications such as heart failure or a sometimes irreversible brain lesion known as central pontine myelinolysis.

This article is licensed under the Creative Commons Attribution-ShareAlike License. It uses material from the Wikipedia article on "Hyponatremia" All material adapted used from Wikipedia is available under the terms of the Creative Commons Attribution-ShareAlike License. Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.